The use of centrifugal forces to increase the force exerted on pressure plates in clutches is well known in the art of clutch design of the Long-type and the Borg & Beck-type. In the Long-type clutches, centrifugal assistance ordinarily takes the form of weights added to the outward ends of release levers. For example, U.S. Pat. Nos. 2,021,973, 20038,017, and 2,206,988 to Wemp, and U.S. Pat. Nos. 2,163,971 and 2,657,781 to Zeidler disclose clutches of the Long-type which use coil springs (as the primary source of clutch pressure), and release levers with centrifugal weights (as a secondary source of clutch pressure). While these designs effectively increase the pressure exerted on a pressure plate, they do not provide for redistribution of the forces applied by the coil springs (which is desirable to reduce uneven wear, "hot spots" and slippage), and, moreover, these designs are not applicable to all other clutch designs.
Centrifugal weights have also been employed in the Borg & Beck type clutches. In these type of clutches, the centrifugal weights take the form of rollers which roll or slide on the surface of the pressure plate and contact the inside surface of the cover plate. As engine speed increases, the rollers move outward, wedging between the pressure plate and the cover, thereby applying pressure on the pressure plate. As with the Long-type clutches, these designs increase the pressure applied to the pressure plate, but they do not redistribute the forces applied to the pressure plate by the coil springs. Moreover, since the rollers are necessarily loose, they can disintegrate and fly free of the clutch in a "burst" situation.
A type of centrifugal weighting has also been used in the design of diaphragm clutches. In some diaphragm clutches centrifugal weights are affixed to the inner ends of the fingers of the diaphragm springs. The inner ends of the fingers of the spring are bent outward, thereby creating lever arms between the ends of the springs and the fulcrum rings. The centrifugal force generated by the ends of the spring fingers is magnified by this lever arm and acts on the pressure plate. While this design provides for some centrifugal loading, it necessarily does not add a significant amount of centrifugal assist. Moreover, it does not redistribute the forces applied to the pressure plate by the spring.
What is desired, therefore, is a clutch design having a centrifugal assist which distributes the forces applied by the spring, which increases the total forces applied to the pressure plate, and which is highly efficient and safe with a minimum of parts to eliminate possible disintegration.